The present invention relates to apparatus and techniques for magnetic resonance imaging (MRI). More specifically, the present invention relates to magneto-resistive sensor apparatus and magneto-resistive sensor techniques for MRI.
Magnetic resonance imaging (MRI) has become a well-established two-dimensional (2D) and three-dimensional (3D) visualization technology with extensive applicability in clinical medicine and basic research. MRI techniques provide detailed images of structures inside bodies and samples that exceed the level of image detail currently provided by x-ray techniques. Further, MRI techniques do not introduce the deleterious effect on a body or a sample that the ionizing radiation of x-ray techniques introduce.
Improvements in imaging resolution of MRI have steadily progressed in the last three decades from the relatively crude images generated by early MRI machines to the current spatial resolution of relatively modern MRI machines. The current spacial resolution provided by modern MRI machines is approximately 1 micrometer of resolution. The resolution of MRI stands in contrast with other imaging technologies, such as electron microscopy and various scanning probe microscopies that provide resolution down to the atomic level.
MRI techniques generally include applying an initial polarizing magnetic field to a sample (e.g., body, scientific sample, etc.) to generate an image of the sample. A radio frequency (RF) magnetic field is also applied to the sample, which is relatively small compared to the polarizing magnetic field. The RF magnetic field is applied to the sample generally perpendicular to the polarizing magnetic field. At a resonant frequency of the RF magnetic field, magnetic resonance of nuclear spins and/or electron spins can be observed as the spins precess. Magnetic resonance signals have traditionally been detected by inductive coils, mechanical detectors, and Hall sensors. While these detectors have been used extensively for magnetic resonance detection, the resolution of these sensors is limited. For example, coil detectors often lack sufficient sensitivity to detect relatively weak magnetic resonance signals and therefore lack the resolving power to resolve these weak signals.
Other resolution limiting factors of traditional MRI techniques include the magnetic field gradients that are applied to samples to image spatial spin distributions. Traditional magnetic field gradients often lack relatively high magnetic imaging gradients sufficient for relatively high MRI resolution.
Therefore, new MRI apparatus and techniques are needed that provide relatively high MRI resolution, are simple and inexpensive to manufacture, and are relatively simple to use.